/*
 * Copyright (c) 2007 innoSysTec (R) GmbH, Germany. All rights reserved.
 * Original author: Edmund Wagner
 * Creation date: 29.05.2007
 *
 * Source: $HeadURL$
 * Last changed: $LastChangedDate$
 *  
 * the unrar licence applies to all junrar source and binary distributions 
 * you are not allowed to use this source to re-create the RAR compression algorithm
 * 
 * Here some html entities which can be used for escaping javadoc tags:
 * "&":  "&#038;" or "&amp;"
 * "<":  "&#060;" or "&lt;"
 * ">":  "&#062;" or "&gt;"
 * "@":  "&#064;" 
 */
package com.github.junrar.crc;

/**
 * DOCUMENT ME
 * 
 * @author $LastChangedBy$
 * @version $LastChangedRevision$
 */
public class RarCRC
 {

  private final static int crcTab[];
  static
   {
    crcTab = new int[256];
    for (int i = 0; i < 256; i++)
     {
      int c = i;
      for (int j = 0; j < 8; j++)
       {
        if ((c & 1) != 0)
         {
          c >>>= 1;
          c ^= 0xEDB88320;
         }
        else
         {
          c >>>= 1;
         }
       }
      crcTab[i] = c;
     }
   }

  private RarCRC()
   {
   }

  public static int checkCrc(int startCrc, byte[] data, int offset, int count)
   {
    int size = Math.min(data.length - offset, count);
    // #if defined(LITTLE_ENDIAN) && defined(PRESENT_INT32) &&
    // defined(ALLOW_NOT_ALIGNED_INT)
    /*
     * for (int i = 0; (0 < size) && i < data.length - 8 && ((data[i + 8] & 7)
     * != 0); i++) { startCrc = crcTab[(short) (startCrc ^ data[i]) & 0x00FF] ^
     * (startCrc >>> 8); size--; }
     * 
     * for (int i = 0; size >= 8; i += 8) { startCrc ^= data[i + 0] << 24;
     * startCrc ^= data[i + 1] << 16; startCrc ^= data[i + 2] << 8; startCrc ^=
     * data[i + 3];
     * 
     * startCrc = crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8); startCrc
     * = crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8); startCrc =
     * crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8); startCrc =
     * crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8);
     * 
     * startCrc ^= data[i + 4] << 24; startCrc ^= data[i + 5] << 16; startCrc ^=
     * data[i + 6] << 8; startCrc ^= data[i + 7]; startCrc = crcTab[(short)
     * startCrc & 0x00FF] ^ (startCrc >>> 8); startCrc = crcTab[(short) startCrc
     * & 0x00FF] ^ (startCrc >>> 8); startCrc = crcTab[(short) startCrc &
     * 0x00FF] ^ (startCrc >>> 8); startCrc = crcTab[(short) startCrc & 0x00FF]
     * ^ (startCrc >>> 8); size -= 8; }
     */

    for (int i = 0; i < size; i++)
     {
      /*
       * // (byte)(StartCRC^Data[I]) int pos = 0; // pos=0x00000000 pos |=
       * startCrc; // pos=ffffffff
       * 
       * pos ^= data[i]; // data[0]=0x73=115dec --> pos=140
       * System.out.println(Integer.toHexString(pos));
       * 
       * // Only last 8 bit because CRCtab has length 256 pos = pos &
       * 0x000000FF; System.out.println("pos:"+pos); //startCrc >>>= 8;
       * 
       * 
       * //StartCRC>>8 int temp =0; temp|=startCrc; temp >>>= 8;
       * System.out.println("temp:"+Integer.toHexString(temp));
       * 
       * 
       * startCrc = (crcTab[pos]^temp);
       * System.out.println("--"+Integer.toHexString(startCrc));
       */

      startCrc = (crcTab[((int) ((int) startCrc ^ (int) data[offset + i])) & 0xff] ^ (startCrc >>> 8));

      // System.out.println(Integer.toHexString(startCrc));

      // Original code:
      // StartCRC=CRCTab[(byte)(StartCRC^Data[I])]^(StartCRC>>8);
     }
    return (startCrc);
   }

  public static short checkOldCrc(short startCrc, byte[] data, int count)
   {
    int n = Math.min(data.length, count);
    for (int i = 0; i < n; i++)
     {
      startCrc = (short) ((short) (startCrc + (short) (data[i] & 0x00ff)) & -1);
      startCrc = (short) (((startCrc << 1) | (startCrc >>> 15)) & -1);
     }
    return (startCrc);
   }

  // public static void main(String[] args)
  // {
  // RarCRC rc = new RarCRC();
  // //byte[] data = { 0x72, 0x21, 0x1A, 0x07, 0x00};
  //
  // byte[] data = {0x73 ,0x00 ,0x00 ,0x0D ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00
  // ,0x00};
  //
  // int crc = 0x90CF;
  //
  //
  // int result = rc.checkCrc(0xFFFFffff, data,0,data.length);
  // System.out.println("3: "+Integer.toHexString(~result&0xffff));
  //
  // }

 }
